The LM1937 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant
current.
The device can drive two, three or four LEDs in series from a Li-Ion cell.
Series connection of the LEDs provides identical LED currents

resulting in uniform brightness and eliminating the need for ballast
resistors. The output capacitor can be as small as 0.22µF, saving space versus alternative solutions. A low
95mV feedback voltage minimizes power loss for better efficiency.